The Hessens took heavy losses during the invasion of New Hessen during the Fourth Succession War; both the Second New Hessen Irregulars and the New Hessen Armored Scouts were destroyed, while the First lost two out of three battalions, with the third battalion retreating.[2] The Armed Forces of the Federated Suns had dropped both regiments of the New Ivaarsen Chasseurs on New Hessen in the first wave of Operation RAT.[3] The timing of the attack was unfortunate for the Irregulars - normally, there would be several regiments training on New Hessen at any given point in time, as the planetary nobility rented out the wide expanses of open plains and mountains to the CCAF for training, but the timing of the Chasseurs attack brought them to New Hessen when only the light Irregulars regiments were on the planet. The First Irregulars attempted to outmaneuver the First Chasseurs on the Joburg Plains, but the Chasseurs had the advantage in terms of the number of available aerospace fighters and those fighters kept the Irregulars pinned in place until the First Chasseurs' ground forces arrived. Meanwhile, the Second Irregulars were outmatched and crushed by the Second Chasseurs in a battle fought within the boundaries of Buchvaal, the planetary capital city.[4]

The First New Hessen Irregulars would be reconstituted shortly before the Jihad. Their first contract was with the LAAF to garrison Thorin. When the Jihad started a few months later, the Word of Blake destroyed much of Hampton's Hessians. The survivors were ordered to Galatea, where they linked up with the rest of the Hessen Irregulars. The Hessen Irregulars made plans to return to New Hessen, and took many smaller mercenary units and civilians with them. The trip took many months, because the Hessans lacked complete JumpShip assets, but as they faced Blakist forces, casualties quickly reduced the flotilla's size. Their largest loss took place in the New Canton system, where the Irregulars were forced to abandon a battalion of friendly troops. A few weeks later they arrived at New Hessen and found a strong garrison in place. The local government had built up a massive defense garrison, and the Hessans were quickly rebuilt. They then jumped to New Canton and dropped every BattleMech into the Blakist's garrison and re-education camps while fighters destroyed static defenses and opened holes in the camp walls. As the Irregular's DropShips landed outside the city, General Hampton led a fighting withdrawal to protect the refugees from the Word of Blake forces. The brutal close range fighting cost the Irregulars a battalion of troops, but they rescued the battalion of soldiers they had to abandon earlier and hundreds of refugees.[5]